Mechanical flexion and extension wrist



Oct. 27, 1953 Q B, ROB|N$0N i 2,656,546

MECHANICAL `FLEXl-.ON AND EXTENSION WRIST Il Filed July 2, 1952INVENTORz George B Rob/nso Patented Qct. 27, 1953 OFFICE MECHANICALFLEXIoN AND EXTENSION WRIST George B. Robinson, Napa, Calif.

Application July 2, 1952, Serial No. 296,980

4 Claims. (Cl. 3-12.4)

(Granted under Title 3-5, U. S. `Code (1952),

sec. 266) The invention described herein may be manufactured and used byand for the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to prostheses and, more particularly, to amechanical flexion and extension wrist.

Prior art prostheses attempting simulation of natural hand and wristmovements, have either been unduly complicated or have failed entirelyto provide certain functions available in the natural member. An objectof this invention is, therefore, to provide an artificial upperextremity of simple construction, which will be capable of ilexion andextension cf the wrist and, in addition, will be applicable to a handwherein flexion and extension of the wrist automatically provides forsimultaneous desired movements of the thumb relative to the palmarportion of the hand.

Other objects and many oi the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. l is a plan view of an artificial hand embodying the principles ofthe invention;

Fig. 2 is a fragmentary view showing the Wrist of the present invention;and

Fig. 3 is a longitudinal cross-sectionl view of an artiiicial armincluding the flexion and extension wrist of this invention.

Reference is made -to the drawings wherein the numeral I indicatesgenerally the artificial hand of this invention. The hand includes arocker I that is pivotally connected to the wrist I2 by means of a pairof spaced parallel arms I4 and I6, corresponding ends of which are xedlymounted in the wrist. Arms I4 and I6 are provided with aligned aperturesand rocker I0 is also provided with aligned apertures through respectivesets of which, bolts I8 and 20 are passed to constitute axles forpivotally mounting the rocker on the spaced arms. The arm I6 includes anextended offset portion 24 for a purpose to be hereinafter described.

Considering the rocker III in more detail, it is seen to comprise fourspaced, sector-like plates 26, and an arcuate mounting plate 28interconnecting the plates 26. Plates 26 are arranged in pairs, one pairof which flanks and is pivotally connected to arm i4, while the otherpair lianks and is pivotally connected to arm I6. Plate 28 is perforatedto form a plurality of locking apertures 30 adapted to receive a lockingpin 32.

Pin 32 is longitudinally displaceable within a bore formed through wristI2 and is biased distally into locking position by means of spring 34bearing against washer-like disc 35 xed to pin 32. The proximal end ofpin 32 is provided with an eye 33 for attaching a control cable 38 whichcable is connected between the eye 36 and a point 39 on the eccentricplate 40, which point is eccentric to the elbow axis (Fig. 3). The plate40 is normally iixed relative to the upper arm by means of a set screw4I engaging the elbow pin which is non-rotatably mounted in the upperarm.

It will be seen that the distance between the point 39 and the wrist I2is at its minimum when the arm is as shown in Fig. 3, exed at degrees.In the construction shown, the length of the cable 38 plus the pin 32 ismade just suicient so that the pin 32 engages the apertures 30. Thus,when the arm is either flexed or extended away from the position shownin Fig. 3, the distance between the wrist and the point 39 increasesand, since the cable-pin link is inextensible, it becomes too short tospan the entire distance and thus, in elTect, is withdrawn fromengagement with the aperture 30 in the rocker I0. The eccentricity ofthe point 39 and the length of the cable 33 are so related that the pinwill be completely withdrawn from its normal locking position when theforearm is either fully extended or fully flexed. This is, of course, amatter of choice, and any other unlocking position can readily beobtained by displacement of the plate 40 through a desired angle.

It will be apparent that the angular position of rocker I0 relative towrist I2 will be determined by the particular one of the lockingapertures 30 in which the pin 32 is seated. It will also be apparentthat the pin 32 can be withdrawn from its seated position by means ofthe cable 38, acting in case of flexion or extension of the forearm, andthat the rocker III can then be moved by flipping the hand or by cableaction or otherwise, so as to align a different locking aperture 30 withthe pin. The exion and extension of the wrist is used to control thumbmovement in the manner to be described. In flexion it is desirable thatthe thumb be swung into opposition with the palmar portion, and inextension it is desirable that the thumb be brought out of opposition tothe palmar portion, the hand thus effecting a grasping movement inflexion and a releasing movement in extension. To accomplish thisfunction, the structure in the illustrated embodiment includes a thumb,generally indicated at 32, having a rst phalange 44, attached by meansof a rubber shank 46 to a proiection 48 formed integral with the rockerI 0. An intermediate point on the phalange 44 is connected to the end ofoffset portion 24 by a flexible cable 50, while its distal end isconnected to the palmar portion 52 by means of a rubber bridge 54. Aspreviously described, the arm i6 and hence its offset portion 24 arefixed relative to wrist I2, whereas the rocker I0 is angularlydisplaceable relative thereto. Thus, as the palmar portion 52 moves inthe direction of flexion the thumb is swung into opposition with thepalmar portion. Similarly, the thumb is swung away from the palmarportion when the palmar portion is moved in the direction of extension.This result is achieved by virtue of the fact that the rubber bridge 54and the rubber shank 4B act on the thumb in such a way as to keep thecable 59 always in tension and, since the cable 50 is in'- extensible,its point of attachment on the thumb must always remain the samedistance from its point of attachment on member I6. Thus, as the base ofthe thumb moves upwardly or downwardly with the rocker l0, the distalend of the first phalange of the thumb, by twisting the shank, swings inan arc to maintain the points of attachment always equidistant.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as snecically described.

What is claimed is:

l. A prosthesis comprising a wrist member;

a hand; means for pivotally mounting said hand relative to said wrist;means for locating said hand in a plurality of angularly displaced positions relative to said wrist, said locating means including alongitudinally displaceable locking pin concentrically positioned toextend through said wrist, and spring means for biasing said pin intoengagement with said hand; and means for disengaging said pin from saidhand in opposition to said spring means comprising an eccentric plateiixed to the upper arm of the prosthesis, concentric with the axis ofthe elbow, a tension member connected at its one end to said pin and atits other end to a point of said eccentric plate located eccentricallyof the elbow axis, the length of said tension element being so relatedto the eccentricity of said point that said pin will be disengaged from'said hand at at least one location when the forearm of said prosthesisrotates from a position of full iiexion to a position of full extension.

2, rihe prosthesis of claim l including means for adjusting about theaxis of the elbow the location of said eccentric point of attachment ofsaid tension member thereby varying the place at which disengagement ofsaid pin will Occur.

3. rIhel prosthesis of claim 1 wherein said hand includes a thumb andpalmar portion, and means for automatically moving said thumb intoopposition with said palmar portion when said hand is iiexed and formoving said thumb out of opposition with said palmar portion when saidhand is extended.

4. A prosthesis comprising an upper arm, a forearm articulated to theupper arm, an arti- :ncial hand and wrist combination including meansfor locking said hand in a plurality of angularly displaced positionsrelative to said wrist, means responsive to the rotation of the forearmrelative to the upper arm for operating said locking means, saidrotation responsive means comprising a plate mounted for adjustmentabout the elbow axis and releasably iixed to the upper arm,- a cableconnected between a point on said plate eccentric to the elbow axis andthe control element of said locking means, the length of said cablebeing so related to the eccentricity or the said eccentric point thatsaid locking means passes through at least one unlocked position as saidforearm rotates from a position or" full exion to a position of fullextension.

GEORGE B. ROBINSON.

References Cited in the ille of this patent UNITED STATES PATENTS StoneOct. 14, 1947

